linux-kernel - Re: [PATCH v5] mm/vmstat: add events for ksm cow

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Message-ID: <624656c7.1c69fb81.9e8ee.5657@mx.google.com>
Date:   Fri, 1 Apr 2022 01:35:00 +0000
From:   CGEL <cgel.zte@...il.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>
Cc:     akpm@...ux-foundation.org, david@...hat.com, willy@...radead.org,
        corbet@....net, yang.yang29@....com.cn, yang.shi@...ux.alibaba.com,
        dave.hansen@...ux.intel.com, saravanand@...com, minchan@...nel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, jhubbard@...dia.com,
        xu xin <xu.xin16@....com.cn>,
        Ran Xiaokai <ran.xiaokai@....com.cn>
Subject: Re: [PATCH v5] mm/vmstat: add events for ksm cow

On Thu, Mar 31, 2022 at 06:44:31PM +0700, Bagas Sanjaya wrote:
> On 31/03/22 10.56, cgel.zte@...il.com wrote:
> > +Monitoring KSM events
> > +=====================
> > +
> > +There are some counters in /proc/vmstat that may be used to monitor KSM events.
> > +KSM might help save memory, it's a tradeoff by may suffering delay on KSM COW
> > +or on swapping in copy. Those events could help users evaluate whether or how
> > +to use KSM. For example, if cow_ksm increases too fast, user may decrease the
> > +range of madvise(, , MADV_MERGEABLE).
> > +
> 
> Did you mean "tradeoff between possible delay on KSM COW and swapping
> in copy"?
>
I mean both are tradeoff, or in other words KSM sacrifices time to gain space.
KSM COW please see do_wp_page(), KSM swapping in copy see ksm_might_need_to_copy().

Thanks.
> -- 
> An old man doll... just what I always wanted! - Clara